Sorrell was cautious when asked if the agency model is facing structural pressures.

"You’ve seen enough announcements about what is happening to agency costs to know there are pressures in the system," Sorrell said, without naming specific clients because it would be "invidious" to name them and they don’t want to be identified.

However, it is well known that Procter & Gamble and Unilever have both cut the number of agencies they use and production fees across the ad industry.

He said later during his investor presentation: "There’s got to be some cyclical stuff and some structural stuff."

Other big ad groups have talked about a stronger second half of the year in 2018 but Sorrell did not want to be too optimistic in his forecasts.

Paul Richardson, WPP's finance director, added: "One of the businesses we do see significant pick-up is the media business."

There has been talk of a "Mediapalooza 2" with a string of media reviews, including HSBC, Shell and Mars, but Sorrell said: "On Mediapalooza, I don’t think it’s enormously stronger than we’ve seen on a consistent basis [over the last few years]."

WPP has been merging many of its agencies to simplify the group and save money.

"This is probably the most aggressive we’ve been," Sorrell said, comparing WPP’s restructuring in response to the slowdown to how the group coped with previous slumps in 1990-91, 2000 and 2008-9.

WPP slashed its net acquisition spend – the amount it spent on acquiring agencies, less disposals – to £30m in 2017, from £605m a year earlier, in another sign it is being prudent.